1. Field of the Invention
The present invention generally relates to a retrievable tree cap for use on a concentric bore “conventional” or “vertical” subsea tree. The tree cap may be installed and retrieved using a remote operated vehicle (ROV). The tree cap may include buoyant material, such as syntactic foam, to decrease the submerged weight of the tree cap. The buoyant material may be configured to orient the tree cap in a vertical position when submerged. The tree cap may include a foldable handle that may be used by the ROV to transport the tree cap. The ROV may be used to move the handle from a vertical position to a horizontal position after the tree cap has been installed into the subsea tree. The tree cap may include a hot stab injector that the ROV may remove from the tree cap after installation of the tree cap.
The tree cap may be landed into the concentric bore of a subsea tree and locked in place before setting the seals within the bore. A plurality of seals of the tree cap may be used to hydraulically isolate the annulus bore from the production bore of the tree spool. A hot stab injector may be used to apply fluid pressure to the tree cap to first engage a first locking mechanism to selectively lock the tree cap to the subsea tree and to then the pressure may be used to set or energize a plurality of seals within the bore of the subsea tree. A second locking mechanism may be used to selectively secure a seal carrier in a lower position wherein the plurality of seals isolate the production and annulus bores of the subsea tree.
The tree cap may further include means for injecting a corrosion inhibitor within a cavity of the tree cap. The tree cap may include a flow path and valve, such as a p-trap vent or one-way check valve, which permits the removal of water trapped between the tree cap and the subsea tree. The tree cap may also include a flow path that may be used to pressure test the seals on the seal carrier. The tree cap may be adapted to permit a first locking means to engage a profile of the subsea tree regardless of the radial orientation of the tree cap.
2. Description of the Related Art
A wellhead assembly, such as that employed on the seabed for offshore drilling and production operations, may often include a “conventional” or “vertical” subsea tree used to access the well bore. The subsea tree includes a bore that may be sealed off or isolated using a tree cap. Typically the subsea tree includes a production bore as well as an annulus bore that may be isolated with the insertion of a tree cap. Prior tree caps generally require the specific radial alignment of the tree cap in order to be inserted and secured in the subsea tree. The alignment of the tree cap to a particular radial alignment may be difficult when installing the tree cap with a ROV. It would thus be beneficial to provide a tree cap that may be installed into a subsea tree at any radial orientation.
While installing a tree cap in a subsea tree one potential problem is damaging the seals during the installation process. The seals are the key component to the tree cap so it is important to prevent damage to the seals during the installation process. It would thus be beneficial to provide a tree cap that may be installed and selectively secured to a subsea tree before the seals are set.
The installation of a tree cap on a subsea tree spool can be difficult. A ROV may be used to install the tree cap. It would thus be beneficial to provide a light weight tree cap to facilitate the installation of the tree cap by a ROV. The tree cap may have integral buoyancy to regulate wet weight. The tree cap may have integral buoyancy to help the underwater transport of the tree cap. It may be also beneficial to have integral buoyancy that is configured to orient the tree cap in an upright position when submerged.
Fluid may become trapped within the cavity of the tree cap while the tree cap is installed onto a tree spool. This may be problematic for a light weight tree cap as the fluid may prevent the tree cap from properly landing on the tree spool. Further, the water may cause corrosion of some of the internal parts of the tree cap and subsea tree system such as the VX gasket. It would be beneficial to provide means for releasing trapped fluid from within the cavity of the tree cap. Further, it would be beneficial if this means also allowed for the injection of a corrosion inhibitor within the tree cap.
In light of the foregoing, it would be desirable to provide a tree cap that may be installed in a concentric bore of a subsea tree at any radial orientation of the tree cap. It would also be beneficial to provide a tree cap with integral buoyancy to reduce the submerged weight of the tree cap. It would be beneficial to provide a tree cap that may be selectively secured to a subsea tree prior to setting the seals to isolate the production and isolation bore. It would be beneficial to provide a tree cap that may be first locked to the subsea tree by the application of hydraulic pressure and then may set the seals to isolation the production and annulus bores by the continual application of hydraulic pressure. It would be beneficial to provide a tree cap that orients itself in an upright position when submerged. It would be beneficial that provides a tree cap that permits the removal of water trapped between the tree cap and the subsea tree. It would also be beneficial to provide a tree cap that permits the pressure testing of the seals of the seal carrier.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.